I've got to disagree... the only lego games i've really liked are all the Star Wars ones and Lego Indiana Jones... Lego Batman tried to be more than a Lego game in my opinion and Harry Potter was just a bit of a muddle to me... and I'm a big fan of the films
and books so thought it'd be right up my alley so to speak
Get Lego Harry Potter if you want a good game but as Az said, it doesn't give up its achievements very easily.
The games of the movies however are foul abominations of titles, though the sub-par voice work from some of the 'sound-a-likes' is often hilarious. That being said they do give away gamerscore very easily, it just depends on if you can stand them long enough
to get it all.